Reflotation concentration of sylvite



United States Patent O 3,137,659 REFLQTATN CNCEN'IRATN @il SYLVTE RandalE. and .loseph S. Reiter, Earlsbad, N. Mex., assignors to Potash Companyof America, Carlsbad, N. Mex., a corporation of Colorado Filed Sept. 5,1961, Ser. No. 135,948 6 t'llairns. (Cl. m29-l2) This invention relatesto froth flotation processes, particularly as applied to the treatmentof sylvinite ores forthe concentration of the sylvite content of suchores.

Flotation treatment of potash ores, particularly sylvinite ores, ishighly developed, and commercial treatments have been devised to attaina high degree of concentration of the sylvite content of such ores,which concentrate is of good grade and comprises a marketable product asdischarged from the treatment. The chief ores of sylvite are mixtures ofhalte and sylvite which may contain minor quantities of clay,poiyhalite, anhydrite and other salts. Sylvite is the most valuableconstituent. The present commercial practices for the treatment ofsylvinite ores utilize a rougher-cleaner flotation section, and in theusual treatment the rougher concentrate constitutes the feed to thecleaner section.

It is well known that flotation tests conducted under ideal conditionssuch as in a laboratory or pilot plant will demonstrate that withoptimum size control of the feed, reagent application methods, aeration,agitation rates, and treatment time, substantially complete flotationmay be accomplished with very low collector reagent rates. It is alsowell known that it is very diliicult to attain similar reagent ratesunder the usual refinery or concentrator conditions which areencountered in commercial operations.

In such commercial operations, if the rougher feed is conditioned withthe amount of collector reagent which under ideal conditions will floatsubstantially all of the sylvite content thereof, flotation will beincomplete particularly in the coarser sizes. To achieve satisfactoryflotation of the coarse sizes under such conditions it is necessary toadd substantially more collector reagent. With relation to the linesizes, the additional reagent necessary to assure liotation of thecoarse sizes is waste. This wasting of reagent may be reduced by one ormore of the following practices, viz., careful size range control of thefeed material, separate reagentizing according to size, variations inreagent makeup, or careful control of conditioning and flotationsections.

ln the potash industry, it is noted that products in the coarser sizesare more desirable commercially. Tyler screen sizes are conventionallyused in the industry to indicate product and feed sizes and are usedthroughout this specification. Granular potash in the range of aboutminus 6 plus 14 mesh carries a higher market price than the smallersizes of equivalent grade. Consequently, it is advantageous to grind theore feed so that it contains a high percentage of the coarser sizes. Inmany cases this type of grinding produces some true middling particleswhich are particles consisting partly of KCl (sylvite) and partly ofNaCl (halite). Since the collector reagent is active only as to thesylvite portion of the particle, it will be seen that such particles aremore ditricult to iloat than particles of the same size consistingsolely of sylvite.

The market advantage enjoyed by the coarser sizes has resulted in thepreparation of ore feeds which contain particle sizes from about minus 6mesh ranging downward. The larger sizes of about minus 6 plus l4 meshwhich are dillicult to lioat are more satisfactorily treated in aseparate granular section, while the smaller, more easily ioated sizesof about minus 14 mesh are treated in a separate section, usually calledthe standard section, having reference to the standard size of thematerial being vite.

`treated in otation cells.

3,137,650 Patented .lune 16, 1964 treated therein. It willbe noted thatwhen, due to temporary failures in theore preparation step, particles oflarger size intended for the granular section are introduced into thestandard feed, they will not float under the conditions established forthe treatment of particle sizes intended to be floated in the normaloperation of the standard section.

According to preferred practice of the present invention, the ore feedisY prepared in the conventional manner by grinding in closed circuit topass through a screen of about 6 mesh and then is passed through asizing section where it is separated into two fractions, one designatedGr-anular (about minus 6 plus 14 mesh) and the other designated Standard(about minus 14 mesh), after which the standard feed is scrubbed,deslimed, and conditioned with collector reagent in an amount necessaryto float substantially all of the sylvite under optimum plantconditions. Alternatively, the ore feed may be scrubbed prior to sizingand deslimed prior to sizing. Whereas optimum flotation can beaccomplished in the laboratory under ideal conditions with about .05 lb.amine per ton of ore feed, it will require about '.l lb. of aminereagent per ton of ore feed under optimum plant conditions.

After such conditioning the feed is subjected to rougher dotationtreatment, and the rougher flotation concentrate product is sent tocleaner cells in conventional fashion. The finer sizes of the rougherunderow consist principally of halite with very little sylvite. Thecoarser sizes of the rougher underilow consist of coarse halite, coarsesylvite and coarse middlings.v The middlingsalmost all occur in thecoarser sizes. Such middling particles are more diicult to coat withcollector reagent under refinery or concentrator operating conditionsand will usually fail to float in the rougher flotation section unlesssubstantially more collector reagent is added than would be necessary tofloat only the liner fractions.

We have found that the underflow from the rougher flotation sectionlends itself advantageously to mechanical separation to segregate thecoarse sizes from the fine sizes. This may be conducted in any of theusual devices such as screening, wet classifying' in conventionalcl-assiers or in wet cone separators. We have found that the bestresults are obtained when the separation is at about plus or minus 20mesh but the point of separation may be varied to suit the conditionsencountered in actual practice. As used herein the minus 20 meshfraction will be termed tine sylvite and the plus 2O mesh fraction willbe termed coarse sylvite. Separation should be made at a screen sizewherethe liner fraction contains so little sylvite that it can be sentdirectly to tails. This will usually indicate a liner fractioncontaining not more than'about 1% syl- The classification applied to therougher underilow, effectively separates the tine sized halite from thecoarse sylvite, halite, and middlings so that in addition to performingthe desired classification, the segregation of sizes amounts to at leasta partial separation by chemical composition as well. The effect of thissegregation is to reduce the Volume of pulp being introduced into thelater retreatrnent cycle so that only small capacity equipment isrequired for effective concentration at such stage. The reduced quantityof material being treated affords another benelit in that only a smallquantity of amine reagent introduction is required in the reconditioningfor the later retreatment cycle to insure high recovery of coarsesylvite and middlings.

After size separation of the rougher underiiow into at least twofractions, the coarser fractions are reconditioned with collectorreagent in amounts suicient to iloat substantially all of the sylvitepresent and again The unlloated fraction of this second flotationtreatment will contain such a minor amount of KCl that it is asatisfactory grade of salt for commercial purposes and may be taken as amarket product when the operation is performed in an area where therequisite shipping costs of such product do not price it out of themarket.

f Accordingly, it is an object of this invention to provide a simple,economical and efficient process for the treatment of potash ores torecover high grade sylvite in size ranges providing a substantialquantity in segregated coarse sizes that are well suited for the marketWithout blending or which may be blended with other high grade KCl inner sizes to provide a product which is now recognized as an adequatecoarse KCl product.

Another object of the invention is to provide a simple,

efficient and economical flotation process for concentration of thesylvite content of the Sylvinite ores in which a high grade concentrateis obtained throughout the size range of the sylvite content with aminimum use of collector reagent.

A further object of the present invention is to recover the sylviteproducts which failed first flotation, whether due to improper feedpreparation or improper flotation conditions.

Yet another object of this invention is to provide a novel method offlotation concentration of sylvite permitting preparation of :arelatively coarse feed to the concentration circuit.

Other objects of the invention reside in the provision of novel stepsand treatments for improving concentration in conjunction with reducedreagent consumption.

While the practice of the invention may utilize a variety of equipmentincluding flotation cells, it is particularly advantageous to conduitthe flotation at the reflotation stage in cells of the type shown anddescribed in United States application Serial No. 838,544, and tooperate said cells according to the process disclosure of United StatesPatent No. 2,931,502.

The practice of the invention will be best understood by reference tothe accompanying flow sheet illustrating a typical arrangement ofequipment and treatment steps utilized in the practice of the invention.As shown, ore, such as Sylvinite ore, from a suitable source of supply 1is conducted through a grinding stage 2 and screening or sizing stage 3(here shown as two stages 3A and 3B) to produce feed for separateflotation sections designated Granular Section 4 with feed about minus 6plus 14 Tyler mesh and Standard Section 5 with feed about minus 14 Tylermesh. If desired, screen oversize may be returned for regrinding asshown at 6. Referring to the feed to the Standard Section, the dischargefrom the screening stage 3 is subjected to scrubbing, if necessary, at7, and desliming as indicated at 8 for removal of fine material. Thematerials removed as aforesaid usually have so'little value that theyare wasted as indicated at 9, but When they include sufficient KClcontent to have commercial significance, such slimes may be passed to asubsequent treatment stage (not shown) for recovery ofV the sylvitecontent as brine.

Following removal of the slime content as aforesaid, the clean ore issubjected to a conditioning treatment 10 in which a clay blindingreagent and any of the well known amine collector reagents for sylvitemay be introduced as shown at 11 and 12, respectively. Preferably, thequantity of such collector is limited to the amount required to floatsubstantially all of the sylvite content under optimum plant conditions,usually about .1 lb. of amine collector per ton of ore feed. This amountwill easily float substantially all of the fine fraction of the Standardfeed (under about mesh). The pulp after conditioning as aforesaid isintroduced as feed to the rougher flotation section 13. The rougherconcentrate is taken as feed 14v to the cleaner flotation section 15 inaccordance with prevailing practice.

One of the innovations of this invention relates to treatment of therougher underflow. This underflow 16 is subjected to classification orscreening, preferably screening on sieve bend units 17, and the oversizereject 18 of the screen is conducted to a reconditioning stage 19, andthence to the reotation stage 21 as previously described. The finesdischarge 25 of screening which is fine halite is passed to waste.

It will be observed that if the screening section 3 should malfunctionand the feed to the standard section 5 should contain any granularmaterial usually sized about plus 14 mesh, such granular material willprobably not be floated at 13 but will report with the tailings 16 ofrougher section 13 and will be separated :at 17 for treatment at 19 andfollowing stages. Enough additional amine collector is introduced atreconditioning stage 19 as shown at 20 to insure flotation ofsubstantially all sylvite fractions, but inasmuch as such material hasreceived a substantial coating or filming in the initial conditioningstage 1G, only a slight addition to particle surfaces is necessary torender the coarse particles readily floatable. Consequently, the totalreagent introduction at conditioning steps 10 and 19 is substantiallyless than would be required if an attempt were made to float all sylvitesizes in the rougher flotation stage.

The flotation treatment at the coarse flotation stage 21 may beperformed in any suitable apparatus, such as standard type mechanicalflotation cells, but as noted previously, is preferably performed in ajet cell of the type shown in Patent No. 2,931,502. Most of the stagesdescribed above are carried out with the ore pulped in brine saturatedas to sylvite and halite. Brine will therefore be introduced or removedas required at various stages of the process. These are standardprocedures and are not indicated on the flowsheet but a note about brineaddition is shown. The reflotation underflow comprising halite is passedto waste as shown at 27.

The concentrate 22 of reflotation stage 21 may be leached for upgrading(not shown) before being discharged from the process as product,preferably going through the dewatering stage by which the brine isseparated and held in the plant circuit. The nal stage of the dewateringprocedure will be a drying stage (not shown) so that the final productpassing from the plant is sufficiently dry to permit storage ortransportation as required.

The concentrate 23 of the cleaner stage 15 provides another marketablesylvite product which is also of high grade, butin the standardflotation size range. In usual practice, this will be discharged fromthe plant through a dewatering section of conventional type (not shown)and may be handled as a separate product for sales purposes.. However,all or a part of such concentrate may be conducted for blending with thecoarse KCI product as Vshown at 24 and in the present plant practice, itis customary to have a number of such blends involving different sizeranges, all of which are commercial products for particular purposes.The cleaner underflow may be conducted to waste as shown at 26, recycledto flotation as shown at 28, or otherwise retreated.

In the preceding description, reference has been made to theintroduction of additional collector reagent at 20 in the conditioningahead of the coarse reflotation stage 21. Usually the collector reagentwill be the same composition as introduced into the conditioning stage10, but for certaintypes of ore, it may be preferable to include adifferent amine or an amine-oil mixture as the collector reagentintroduced at reconditioning stage 19.

In order to illustrate the efficiency of the flotation of Sylviniteaccording to this invention, a typical test opera-k tion is reported.Sylvinite ore from the Carlsbad basin wasV used. Screen analysis of theore and of products is shown in the following `chart or tabulation.

Ore weighing 381 grams was pulped with brine and subjected to adesliming treatment for removal of clay and other slime constituents. Inthis operation, 25 grams of slimes were removed. The cleaned ore wasthen conditioned with 0.5 lb. of starch and 0.1 of octadecyl amine perton of ore and a little frother oil. On rougher flotation, 120 grams ofconcentrate were produced as a floated product and 236 grams wereproduced as unfloated residue (rougher underflow). The 236 grams of'unfloated residue (rougher underflow) were screened roughly on a 20 meshscreen producing 135 grams of minus 20 mesh material and 101 grams ofplus 20 mesh material.

The 101 grams of plus 20 mesh material were then reconditioned with .15lb. of amine and 0.8 lb. of a heavy fractionator-bottom oil per ton ofthis coarse flotation feed. On reflotation of the plus 20 mesh material,22.3 grams of coarse concentrate were produced as the floated productand 78.8 grams of coarse tailings were produced as the undoated residue.

Screen analyses of value in interpretation of the results of such testare presented in the following chart. Tyler mesh are used and theproportion on each mesh is given as a percentage.

tion section. Thus, in a plant treating several thousand tons of ore perday, a significant reduction in reagent cost can be effected whilemaintaining a high efficiency in the concentration.

As an alternative procedure, sizing section 3B may be omitted andgranular section d bypassed and all feed sent to standard section 5. Inthis event, the rougher underflow will contain substantial sylvitevalues in the coarser sizes.- The coarse fraction of the rougherunderflow 18` controlling the aeration or agitation rate, or both, in

Feed 9. 3 12.8 18.9 14. 7 10.5 10. 6 7. 7 6. 2 2. 7 4. 5 2.1 1stC0ncentrate 0. 6 5. 0 17. 4 17. 3 13. 9 14. S 9. 8 9. 9 4. 2 3. 4 2. 3Rougher underflow 12. 4 13. 9 18.1 14.1 10.1 10.1 6. 5 6.7 3. 5 2. 9 l.7 lVIluS 20 mesh (RII.) 0. 2 19. 6 18. 5 17.0 14. 6 12. 3 8. 5 5.1 4. 2Plus 20 mesh (R.U.) 26. 3 29. 5 38.1 6.1

In carrying out the operation the following Weights and grades expressedas K2() content were found:

Gn scrubbing the ore for release of slime, some breakage occurred, butit will be noted that the first concentrate was considerably finer insize than the feed and that the rougher underflow was coarser. Onscreening the rougher underflow, the fine fraction (minus 20 mesh) wasof low grade while the coarse fraction (plus 20 mesh) carried 12.88%KZC. This is a fairly good grade of feed, and on reflotation, a coarsetailings carrying 1.06% KZO was produced.

Therefore on a coarse feed and with a minimum consumption of reagentwhich calculates to 0.14 lb. of amine per ton of ore the recovery was78.6 and 13.4 or 92% of the potash in the ore. Tailings account for 1.5and 0.9 or 2.4% of the potash. The chief loss is with the slimes whichcan be recovered by conventional solution methods.

ln operation, the first concentrate of grade 59.62 would be refloated ina cleaning stage to bring it up above 60.00% K2() the presentspecification on marketable fertilizer potash. The grade of the coarsematerial which contains appreciable middling material was 54.56% K2O andthis would be leached to bring it up to grade also. However, by thisseparation, the leaching operation is carried out on only a smallproportion of the total concentrates.

Present commercial practice has established that in order to floatmaterial of the large or coarse sizes floated in the test reported aboveat a comparable low tailings rate, the reagent requirement would be from0.2 lbs. amine per ton of ore treated to several times that amount, andwould apply to the total tonnage of feed to the flotarougher flotation13 so that substantially all of the sylvite in the size range of aboutminus 20 mesh is recovered as flotation concentrate overflow product.Coarse fraction 13 may then be treated as indicated at 19 and 21, orsubjected to more thorough aeration and agitation in additional orcontinuing flotation cells.

As still another alternative, if sufficient collector reagent has beenadded at the conditioning step l0 prior to rougher flotation,reconditioning at step 19 may be with a water-immiscible oil followed byan additional or further flotation treatment. Other changes andmodifications may be availed of in the selection and arrangement ofequipment utilized in the practice of this invention, and in theprocedures at the several treatment stages, within the spirit and scopeof the invention as dened in the hereunto appended claims.

We claim:

1. In a continuous froth flotation process for the concentration of thesylvite content of sylvinite ore, in which a deslimed pulp of such oreis subjected to a rougher flotation step utilizing a collector reagentfor sylvite, the improvement which comprises separating substantiallyall the fine sylvite of about minus 20 mesh sizes of the deslimed pulpas a froth concentrate in the rougher flotation step, subjecting theunderflow solids of said flotation step to a size separation step forsegregation of a fraction of about plus 20 mesh sizes, reconditioning'said plus 20 mesh fraction so segregated with a sylvite collector,subjecting the pulp so conditioned to another flotation step, andrecovering most ofthe coarse sylvite content of about plus 20 mesh sizesin the rougher flotation underflow as a concentrate of the latterflotation step.

2. ln a continuous froth flotation process for the concentration of thesylvite content of a sylvinite ore, in which a deslimed pulp of such oreis subjected to a rougher flotation stage, the improvement whichcomprises conditioning said pulp with an amine collector reagent forsylvite in an amount required to float substantially all of the sylvitecontent except coarse sizes of about plus 20 mesh at said rougherflotation stage, subjecting the underflow solids of said rougherflotation stage containing unfloated sylvite to a size separation stepfor segregation of a fraction of about plus 20 mesh sizes containingsubstantially all of the unfloated sylvite of the feed to the rougherflotation step, reconditioning the plus 20 mesh fraction so segregatedwith an amine collector E in an amount suilicient to lloat substantiallyall of the remaining sylvite content, introducing the pulp soreconditioned into a second flotation stage, and recovering most of thecoarse sylvite content of about plus 20 mesh sizes in the rougherflotation underflow as a concentrate of the latter otation stage.

3. In a continuous froth flotation process for the concentration of thesylvite content of sylvinite ore, in which a deslimed pulp of such oreis subjected to a rougher otation step utilizing a collector reagent forsylvite, the improvement Which comprises separating substantially allthe fine sylvite of about minus 20 mesh sizes of the deslimed pulp as afroth concentrate in the rougher otation step, subjecting the underflowsolids of said ilotation step to a size separation step for segregationof a fraction of about plus 2O mesh sizes, reconditioning the plus 20mesh fraction so segregated with a sylvite collector, subjecting thepulp so conditioned to a second flotation step, recovering most of thecoarse sylvite content of about plus 20 mesh sizes in the roughernotation underow as a concentrate of said second notation step as a naliiotation product, subjecting the rougher concentrate to a cleanerotation step, recovering a sylvite concentrate of said cleaner flotationstep, and combining said tine concentrate with said coarse sylviteconcentrate as a nal sylvite product.

4. In a continuous froth flotation process for the concentration of thesylvite content of sylvinite ore, in which a deslirned pulp of such oreis subjected to a rougher flotation step, the improvement whichcomprises conditioning said pulp for said flotation step with acollector reagent for sylvite to oat substantially all said sylvitecontent except coarse sizes of about plus 20 mesh, separatingsubstantially all the fine sylvite of about minus 20 mesh sizes of theconditioned pulp as a froth concentration in the rougher flotation step,subjecting the underlioW solids of said rougher flotation step to a sizeseparation step for segregation, removal and discard of a ne fractioncontaining a minor portion of the sylvite in said underflow solids froma coarse fraction of about plus 20 mesh sizes, reconditioning theseparated coarse fraction with a collector in an amount suicient tofloat substantially all of the remaining sylvite content, subjecting thepulp so reconditioned to a second flotation step, and recovering most ofthe coarse sylvite content of about plus 20 mesh sizes in the rougherflotation underflow as a concentrate of said second flotation step.

5. A continuous froth flotation process for the concentration of thesylvite content of sylvinite ore, which comprises subjecting a deslimedpulp of sylvinite ore in a mixed size range of about minus 14 mesh to arougher flotation step utilizing a collector reagent for sylvite forseparating substantially all the sylvite content except coarser sizes ofabout plus 20 mesh as a concentrate, subjecting the underiiow solids ofsaid flotation step containing unlloated coarse sylvite to a sizeseparation step for segregation of a fraction of about plus 2O meshsizes containing substantially all of the unoated sylvite of the feed tothe rougher flotation step, reconditioning said plus 20 mesh fractionwith a sylvite collector, and subjecting the reconditioned pulp toanother otation step for recovering most of the unfloated sylvite in therougher flotation underflow as a concentrate of the latter flotationstep.

. 6. A continuous froth flotation process for the concentration of thesylvite content of sylvinite ore, which comprises subjecting a deslimedpulp of sylvinite ore in a mixed size range of about minus 14 mesh to arougher flotation step utilizing a collector reagent for sylvite forseparating substantially all the sylvite content except coarser sizes ofabout 20 mesh as a concentrate, subjecting the underflow solids of saidiotation step containing unfloated coarse sylvite to a size separationstep for segregation of a fraction of about plus 20 mesh sizescontaining substantially all of the unfloated sylvite of the feed to therougher flotation step, reconditioning said plus 20 mesh fraction with asylvite collector, subjecting the reconditioned pulp to anotherflotation step for recovering most of the unlioated sylvite in therougher notation underow as a concentrate of the latter flotation step,and combining the concentrate of both iiotation steps as a nal sylviteproduct in the size range of the feed to the rougher flotation step.

References Cited in the tile of this patent UNITED STATES PATENTS2,136,341 Hedley Nov. 8, 1938 2,340,523 Ferris Feb. 1, 1944 2,420,476Greene May 13, 1947 2,633,241 Banks Mar. 31, 1953 2,721,657 Smith Oct.25, 1955 2,806,598 Brown Sept. 17, 1957 2,931,502 Schoeld et al Apr. 5,1960 l2,950,007 Smith Aug. 23, 1960 2,984,348 Adams et al. May 16, 1961

1. IN A CONTINUOUS FROTH FLOTATION PROCESS FOR THE CON
 1. IN ACONTINUOUS FROTH FLOTATION PROCESS FOR THE CONCENTRATION OF THE SYLVITECONTENT OF SYLVINITE ORE, IN WHICH A DESLIMED PULP OF SUCH ORRE ISSUBJECTED TO A ROUGHER FLOTATION STEP UTILIIZING A COLLECTOR REAGENT FORSYLVITE, THE IMPROVEMENT WHICH COMPRISES SEPARATING SUBSTANTIALLY ALLTHE FINE SYLVITE OF AOBUT MINUS 20 MESH SIZES OF THE DESLIMED PULP AS AFROTH CONCENTRATE IN THE ROUGHER FLOTATION STEP, SUBJECTING THEUNDERFLOW SOLIDS OF SAID FLOTATION STEP TO A SIZE SEPARATION STEP FORSEGREGATION OF A FRACTION OF ABOUT PLUS 20 MESH SIZES, RECONDITIONINGSAID PLUS 20 MESH FRACTION SO SEGREGATED WITH S SYLVITE COLLECTOR,SUBJECTING THE PULP SO CONDITIONED TO ANOTHER FLOTATION STEP, ANDRECOVERING MOST OF THE COARSE SYLVITE CONTENT OF ABOUT PLUS 20 MESHSIZES IN THE ROUGHER FLOTATION UNDERFLOW AS A CONCENTRATE OF THE LATTERFLOTATION STEP.